The analytical spectral region for measurement of gases, vapors, and volatile materials relevant—for example only—to oil, gas, and other applications extends from the ultraviolet (UV) to the mid infrared (mid-IR) spectral regions. Because of this, many applications rely upon infrared gas analyzers that are used for continuously measuring the real-time concentration of each component in a gas sample that contains various gas components by selectively detecting the amounts of infrared radiation absorbed by the gas components. Infrared gas analyzers are widely used in various fields because of their excellent selectivity and high measuring sensitivity.
Non-dispersive infrared (NDIR) techniques for the analysis of gases for individual species monitoring is one common technique used for an infrared gas analyzer. Traditional NDIR instruments primarily involve mechanical elements, such as filter wheels that are used in the selection of specific filters and their location relative to the optical path between the light source, the sample, and the detector. These commercially available systems are classified as instruments or analyzers.
Single-beam and two-beam (double beam) NDIR gas analyzers are available. With single-beam devices, the infrared radiation generated by the infrared emitter is routed after modulation, such as by a rotating diaphragm wheel, through the measuring vessel containing the gas mixture with the measuring gas component to the detector device. In one example configuration for two-beam devices, the infrared radiation may be subdivided into a modulated measuring radiation passing through the measuring vessel and into an inversely-phased modulated comparison radiation passing through a comparison vessel filled with a comparison gas. In such examples, optopneumatic detectors filled with the gas components to be verified and comprising one or more receiver chambers arranged adjacent or to the rear of one another are usually used for the detector device. Such an approach is sometime referred to as infrared gas filter correlation spectroscopy.
Other traditional methods of for analysis of multi-component gas and vapor monitoring include the use of Fourier transform infrared (FTIR) spectroscopy and gas chromatography (GC). FTIR spectroscopy relies heavily on measuring the spectra of the key components and then relying on spectral resolution or mathematics to separate and measure the individual contributions from the components. Gas chromatography physically separates the components by the chromatograph and the separated components are measured directly from the chromatogram by a suitable detection system; such as a flame ionization detection (FID) system. While both of these are standard reference methods, they are both expensive and may generate a significant service or operating overhead when implemented in a continuous monitoring system, particularly in the case of GC, which requires the use of high purity compressed gases. Similarly, mass spectrometry is another method for analyzing multi-component gas and/or vapor analysis that works by measuring the mass-to-charge ratio and abundance of gas-phase ions within a high vacuum. This method is also costly and hard to reduce to a scalable sensor that can be used for commercial sensing aspects.
Other spectroscopy methods used in monitoring fluids include those disclosed in U.S. Pat. No. 7,339,657 to Coates et al., which is incorporated herein by reference. These examples feature near infrared light-emitting diodes (LEDs) are used for oil condition measurements (soot level) and urea. The soot measurement is a simple photometric measurement with one primary wavelength (940 nm), while the urea quality sensor is a true spectral measurement with a three-point determination having two analytical wavelengths, 970 nm and 1050 nm, for water and urea, and one as reference/baseline, 810 nm. In both cases attenuation of signal intensity is used to compute the infrared (near-infrared) absorption, and this is correlated to the concentrations of soot (in oil) and the relative concentrations of water and urea in the binary mixture/solution.
LED components are available that support an extended spectral region from the UV region to around 250 nm and mid-IR from the about 3 to about 5 micron region. These devices are currently expensive, and do not have a good usable lifetime in the context of low-cost automotive sensors. Both of these LED regions are important for the application to gas and vapor sensing. The mid-infrared is an established region for gas and vapor monitoring, primarily the combustion gases, CO and CO2, and to some extent NOx and other pollutant gases. However, some other NOx gases and other vapors have a spectral range in the UV region that these LEDs cannot adequately reach.
However, existing LED sensing platforms are not reliable for high temperature gas monitoring, and the implementation relative to the optics required is difficult, if not impossible. While using a NDIR concept as a dedicated sensor is feasible, it is not practical because a long physical optical path is required for IR detection, and major combustion gas components, such as carbon dioxide (CO2), carbon monoxide (CO) and water, are all infrared absorbers. Water in particular can become a matrix interferent and prevent accurate readings.
Additionally, commercial artificial noses may be used to determine the components of a gas or vapor sample. These artificial noses are based on the responses of an array of conductive polymers that are correlated to smells and odors of gases and vapors. These are expensive devices, are easily contaminated, and are inferential relative to the smell or odor of the vapor. Unlike the spectral nose function of the present invention, these artificial noses have no direct correlation to the actual function of the human nose.
There exists a need to provide the same functionality of the instruments and analyzers described above but within a single electronic package, where the source, sample, and detector are reduced into the size of a sensor package. Additionally, there is a need to provide a sensor that is capable of monitoring a wide spectral band from the UV to the mid-infrared regions. The present invention can be used in a wide variety of industries where gas sensing and monitoring is critical, especially related to the analysis, safety, and measurement of gases and vapors. The present invention also provides a much broader spectral sensor package for vapors, gases, and other materials that were not previously capable of being monitored in a cost efficient manner.